It has been known that organic materials such as thermoplastic resin, thermosetting resin, natural or synthetic rubber, mineral oil, lubricating oil, adhesive, paint, etc. are deteriorated by an action such as heat, oxygen, etc. on production, processing and use to cause deterioration of the strength of the organic material due to a phenomenon (e.g. molecular cleavage, molecular closslinking, etc.), change in flow properties, coloring, deterioration of surface physical properties, etc., which results in decrease of a commercial value. It has hitherto been known that the organic material is stabilized by containing various phenol and phosphorous antioxidants for the purpose of solving these problems about heat deterioration and oxidization deterioration.
As the phosphorous antioxidant, for example, tris(2,4-di-t-butylphenyl)phosphite is used.
However, these known phosphorous antioxidants had a problem that the stabilizing effect to heat deterioration and oxidization deterioration is insufficient.
On the other hand, eight-membered ring phosphites such as 2,10-dimethyl-4,8-di-t-butyl-6-{2-3-(3-t-butyl-4-hydroxy-5-methylphenyl)p ropionyloxy!ethyl-12H-dibenzod,g!1,3,2!dioxaphosphosin and the like, on which a phenyl group is substituted through a connecting group, an alkylcarbonyloxyalkyl group, have been proposed as means for solving these problems of the phosphorous antioxidant (JP-A-5-86084). However, the stabilizing effect of these eight-membered ring phosphates is not necessarily sufficient, although it has improved.
Six-membered ring phosphites such as 2,4-di-t-butyl-6-3,5-di-t-butyl-6-((6H-dibenzoc,e!1,2!oxaphosphorine-6- yl)oxy)benzyl!phenol, on which a phenyl group is substituted directly, have also been proposed (JP-A-5-222250, JP-A-5-222256, JP-A-5-331313). However, there is a problem that it is liable to color the organic materials.
The present inventors have produced various phosphorous compounds and studied intensively about them. As a result, it has been found that specific six-membered ring phosphonites, on which a phenyl group is substituted through a connecting group, exhibit not only stabilizing effects same to or superior to those of the eight-membered ring phosphites mentioned but also superior anti-cloration effect to that of the above-mentioned six-membered ring phosphites, on which a phenyl group is substituted directly. Thus, the present invention has been accomplished.